1. Field of the Invention
The invention relates to a bubble level that employs electro-optical components for achieving high precision.
2. Description of the Related Art
A typical carpenter's level is an elongated generally rectangular structure having opposed first and second ends. Planar top and bottom faces are aligned parallel to one another and extend between the ends. The top and bottom faces are the portions of the prior art level that will be placed against another surface for assessing horizontal or vertical alignment.
A typical prior art level includes a glass tube partly filled with a liquid spirit. The portion of the tube that is not filled by the liquid forms a bubble. Movement of the level will cause the liquid to shift within the tube, and hence will cause a repositioning of the bubble. The tube includes a pair of lines that are spaced apart by a distance approximately equal to the length of the bubble. When the tube is aligned horizontally, the liquid will be disposed symmetrically in the tube, and the bubble will be positioned precisely between the lines.
The prior art level can be used by placing the top or bottom face of the level on a substantially horizontal surface. The relative position of the bubble in the tube provides an indication of the closeness of the level to a horizontal alignment. The surface on which the level is supported may be adjusted to position the bubble between the lines of the tube, and hence to achieve a fairly exact horizontal alignment of the surface on which the level is supported.
The precision that can be obtained with the prior art level is dependent upon the eyesight of the user and the ability of the user to determine the positions of the ends of the bubble relative to the lines on the glass tube. This ability will depend at least partly upon the optical alignment of the user of the level relative to the bubble tube. Precision can be fairly good if the user has good eyesight and if the user can be positioned so that the line of sight is perpendicular to the axis of the tube. However, the realities of a construction or manufacturing site often do not permit the user of a level to be positioned perfectly relative to the bubble tube. Thus, the level may be positioned at a location significantly above the head of the user or at a position where the line of sight is at an acute angle to the axis of the bubble tube. Either of these fairly common uses of a level significantly reduce accuracies that can be obtained by the level.
The boundary between the gas and the liquid in the bubble tube is fairly precise. However, the bubble is an elliptoid with curved boundaries. A viewer necessarily sees the curved boundaries between the gas and the liquid in the bubble tube, and hence the boundary between the bubble and the liquid appears as a fairly dark broad line. The apparent width of the line that defines the bubble can lead to a lack of precision by the user. In particular, accuracy will vary depending upon which part of the apparently broad boundary of the bubble aligns with the positioning indicia on the glass tube.
The prior art includes the use of electro-optical devices that attempt to determine the position of a bubble in a level. These devices have taken several forms, but rely primarily on attempts to identify an end or midpoint of the bubble or to identify an angle of the surface of the liquid. The known electro-optical devices used with a bubble level do not provide the desired degree of precision.
In view of the above, an object of the subject invention is to provide a bubble level with significantly increased accuracy.
Another object of the subject invention is to provide a bubble level where accuracy is not dependent upon the angle of viewing.